1. Field of the Invention
The invention relates to an internal combustion engine with controlled ignition and direct injection.
The invention relates more particularly to an internal combustion engine with controlled ignition and direct injection of the type in which a cylinder is bounded axially at the top by a lower face of a cylinder head, into which there open, each via a corresponding valve, at least one intake duct and at least one exhaust duct, the intake and exhaust valves being provided respectively on opposite sides of a reference plane containing the cylinder axis and bounding an intake side and an exhaust side of the cylinder.
2. Discussion of the Background
The use of direct injection in internal combustion engines with controlled ignition makes it possible to optimize engine operation with xe2x80x9cleanxe2x80x9d mixtures, or in other words carburetted mixtures in which there exists a large excess of air relative to the quantity of fuel introduced into the cylinder.
The use of lean mixtures makes it possible in particular to greatly lower fuel consumption and also to lower the maximum temperature attained during combustion, in turn making it possible to reduce the production of pollutants such as nitrogen oxides (NOx).
Similarly, the excess of air makes it possible to prevent the situation that part of the fuel remains unburned and is evacuated with the exhaust gases after combustion.
The carburetted mixture resulting from injection of fuel into the cylinder can be a homogeneous mixture or a stratified mixture in which the air-to-fuel ratio is not constant throughout the entire cylinder. For example, it may be desirable to obtain a higher fuel concentration in the vicinity of the spark plug, in order to facilitate starting of combustion.
Different solutions are known which make it possible to achieve stratified charges by means of direct injection.
A first solution comprises positioning the injector and spark plug such that the fuel jet is sprayed directly by the injector toward the spark plug. This method is a priori highly efficient, but it may be sensitive to uncertainties in positioning of the different elements and even more so to possible fouling of the injector nozzle, which can greatly modify the characteristics of the fuel jet.
A second known solution comprises achieving stratification by wall effect, wherein the fuel jet is directed toward a wall, for example the upper face of the piston, after which it is deflected toward the spark plug. An engine using this solution is described, for example, in European Patent A 0558072. Nevertheless, with this solution, considerable fuel condensation takes place on the walls, and the fuel condensed in this way is then very difficult to ignite.
The object of the invention is therefore to provide a general solution with regard to the geometry and layout of the essential elements of an internal combustion engine with controlled ignition, in such a way that optimal engine operation can be achieved with stratified xe2x80x9cleanxe2x80x9d charges.
Toward this objective, the invention proposes an engine of the type described in the foregoing, characterized in that at least one of the intake ducts is adapted to create in the cylinder, at least during certain stages of operation of the engine, a xe2x80x9ctumblexe2x80x9d flow in which the gases contained in the cylinder are caused to move rotationally around an axis perpendicular to the cylinder axis and parallel to the reference plane, and in that a fuel injector is located in such a manner that it enters the lower face of the cylinder head such that the fuel jet tends to be intercepted by the portion of the flow circulating in the sense opposite to that of the jet and directed toward a spark plug.
According to other characteristics of the invention:
the cylinder is axially bounded at the bottom by a piston, an upper face of which is provided with a cavity which is disposed eccentrically relative to a first side of the reference plane, and the injector is located on the opposite side to inject the fuel toward the cavity;
the sense of rotation of the flow is such that the movement of the gases is generally centripetal along a bottom wall of the cavity of the piston;
the injector is located substantially at the center of the lower face of the cylinder head;
the fuel is injected along an axis inclined by an angle of less than 30xc2x0 relative to the cylinder axis;
the injector is located in such a manner that it enters an external radial portion of the lower face of the cylinder head;
the fuel is injected along an axis inclined by an angle of more than 50xc2x0 relative to the cylinder axis;
the cavity is provided with a lateral wall element which, in the vicinity of the cylinder axis, has a large slope along the direction of the axis;
the piston is provided with a channel, which is hollowed out in the upper face of the side opposite the cavity, which is oriented parallel to the injection jet of the injector, and which opens into the lateral wall of the cavity;
the upper face of the piston is provided, on the side opposite the cavity, with a boss whose shape is substantially complementary to that of the portion facing the lower wall of the cylinder head, in order to cause a gas-flushing effect during arrival of the piston at top dead center;
the gases contained in the cylinder are caused to rotate counterclockwise relative to a view of the cylinder with the intake valves on the right and the exhaust valves on the left, the concave cavity is eccentrically disposed on the exhaust side of the reference plane, and the injector is located such that it enters the lower face of the cylinder head on the intake side;
the gases contained in the cylinder are caused to rotate clockwise relative to a view of the cylinder with the intake valves on the right and the exhaust valves on the left, the concave cavity is eccentrically disposed on the intake side of the reference plane, and in that the injector is located such that it enters the lower face of the cylinder head on the exhaust side;
the cylinder is provided with at least two intake valves;
the cylinder is provided with at least two exhaust valves;
the cylinder is provided with a single exhaust valve, which is offset transversely relative to the cylinder axis along a first sense of a direction parallel to the reference plane, and the injector is offset along an opposite sense of the said direction parallel to the reference plane;
the axis of the fuel jet is angularly offset relative to a plane perpendicular to the reference plane and containing axis A1;
the fuel jet extends inside a cone whose apex angle is substantially between 30 and 70xc2x0;
the lower face of the cylinder head has the shape of a roof with two inclined spans, which are bounded by a top ridge contained in the reference plane.